Stereospecific polymers of butadiene copolymerized with small amounts of a divinyl compound



United States Patent Q 3,363,659 STEREOSPECIFIC POLYMERS OF BUTADIENECOPOLYMERIZED WITH SMALL AMOUNTS OF A DIVlNYL COMPOUND Norman FloydKeckler, Stow, and Bernard Lars Johnson, Akron, Ohio, assignors to TheFirestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio NDrawing. Continuation-impart of application Ser. No. 170,836, Feb. 2,1962, which is a continuation-in-part of application Ser. No. 133,807,Aug. 25, 1961. This application July 27,1962, Ser. N 0. 213,007

Claims. (Cl. 152-330) This invention relates to stereospecific polymersof butadiene modified by copolymerizing therewith small amounts of adivinyl monomer, blends thereof with rubbery polymers and pneumatictires made therefrom.

This application is a continuation-in-part of Keckler and Johnsonapplication, Ser. No. 170,836, filed Feb. 2, 1962, which is acontinuation-in-part of Keckler and Johnson application, Ser. No.133,807, filed Aug. 25, 1961, both of which applications are nowabandoned.

This invention relates to modified, solid, rubbery, stereospecificpolybutadienes, to methods for the production of such polybutadienes,and to pneumatic tires, the rubbery portions of which are fabricatedpartially or entirely therefrom.

Tire treads comprising the prior art stereospecific, rubbery butadienesdemonstrate greater heat resistance and toughness and are significantlylonger wearing than analogous tire treads manufactured from SBR ornatural rubber. It is now conventional to manufacture pneumatic tiresfrom such polybutadienes, either alone or in the form of blends withnatural rubber, SBR rubber, or stereospecific polyisoprene. It isgenerally considered that for each 1% by weight of prior artstereospecific polybutadiene blended with natural rubber or SBR rubber,the resulting tire tread will be characterized by 1% greater treadwear.Notwithstanding the advantage of the prior art polybutadienes for treadmanufacture, it is apparent that stereospecific polybutadienes ofsubstantially improved properties would contribute substantially to theart. Moreover, prior art stereospecific polybutadienes, at normalhandling temperatures, are characterized by dimensional instabilitymanifested by significant cold flow.

It is aprimary object of this inventon to provide novel and improvedstereospecific polybutadienes.

It is a primary object of this invention to provide modified, rubbery,stereospecific polybutadienes which, as compared with analogous priorart polymers, impart substantially greater wear to tire treadsfabricated partially or entirely therefrom.

. It is a further object of the invention to provide pneumatic tires andtire tread stocks which comprise such modified stereospecificpolybutadienes.

It is another object of the invention to provide tire treads and tiretread stocks which comprise blends of such modified stereospecificpolybutadienes with plastics, resins or other rubbery polymers,including natural rubber, SBR, stereospecific polyisoprenes,polybutadienes, copolymers of butadiene and ethylene-propylenecopolyniers.

It is an additional important object of the invention to provide amodified rubbery stereospecific polybutadiene which is resistant to coldflow.

It is a specific object of the invention to provide a modified rubberystereospecific polybutadiene which demonstrates substantial dimensionalstability throughout handling and storage periods at temperaturesnormally encountered in such handling and storage.

The compositions to which the invention relates comprise rubbery,stereospecific polymers containing not more than about gel selected fromthe group consisting of (A) polymers of butadiene and a trace amount ofa modifying comonomer having at least two terminal =CH groups and (B)polymers of (1) butadiene, (2) a compound containing a terminal =CHgroup, and (3) a trace amount of a modifying comonomer having at leasttwo terminal =CH groups.

The stereospecific polybutadiene portions of the polymers of theinvention contain from at least about 30% to 100% cis 1,4 structure, atotal 1,4 structure of at least about and not in excess of 12% 1,2structure as determined by infra-red analysis. In the preferred polymersthe polybutadiene portion of the polymer molecule contains not more thanabout 10% 1,2 structure, and a total of at least about 1,4 structure.One sub-group of polymers to which the invention relates ischaracterized by a polybutadiene portion which contains at least about85% cis 1,4 content and not more than about 10%, preferably 5%, 1,2content, whereas an alternative subclass of such polymers contains fromabout 30% to about 60% cis 1,4 structure, at least about 85% total 1,4structure, and not in excess of about 10% 1,2 structure, as determinedby infra-red analysis.

The modified rubbery polybutadienes of this invention are produced bywell known techniques utilized in the synthesis of the unmodifiedstereospecific rubbery polybutadienes of the prior art. Such Well knowntechniques comprise polymerization in the presence of ionic catalysts insubstantially non-aqueous, bulk or solution polymerization systems andare modified to produce the novel polybutadienes of the invention onlyto the extent of including an appropriate trace quantity of themodifying comonomer in the polymerization reaction system. Commercialprocesses for the production of such prior art polybutadienes normallyutilize either Ziegler-type or lithium-based catalysts. The use ofZiegler type catalysts to produce rubbery stereospecific polybutadienesis described, inter alia, in Belgian patents 543,292; 575,671, and551,851. The production of similar or analogous polybutadienes in thepresence of lithium-based catalysts is described, inter alia, in FosterUnited States Patents Ser. Nos. 554,351; 544,352, and 605,440.

This invention embraces the disclosed modified stereospecific polybutadienes generically and without regard of the method or catalystutilized in the production thereof. As the art is aware, however, atleast about 90 weight percent of the stereospecific polybutadienestypically produced in the presence of Ziegler catalysts: arecharacterized by an inherent viscosity extending over a range from about'three to about four inherent viscosity units, whereas lithium-basedcatalysts result in stereospecific polybutadienes in which 90% of thepolymer falls within a range of not more than about two inherentviscosity units. One facet of this invention resides in the discoverythat the modified polybutadienes which are produced in the presence oflithium-based catalysts are characterized by an inherent viscosity rangeextending over a range of three to four inherent viscosity unitscomparable to that of the polybutadienes produced in the presence ofZiegler-type catalysts. Generally speaking, therefore, at least about90% by weight of the modified stereospecific polybutadienes of theinvention has an inherent viscosity in excess of 1 and extends over arange of at least 3 and frequently 4 inherent viscosity units.

The invention generically embraces, as modifying comonomers, all organiccompounds which are characterized by two or more reactive, terminal =CHgroups. These organic compounds are effective for the purposes of theinvention in their commercial grades as well as in their purified form.The modifying comonomers to which the invention relates may be eitheraliphatic, aromatic, cyclic, acyclic, or heterocyclic. The preferredcompounds include the benzenes, xylenes, anthracenes, naphthalenes, anddurenes which are substituted by two or more vinyl groups. Specificallypreferred compounds include divinyl, trivinyl, and tetravinyl benzene;divinyl, trivinyl and tetravinyl ortho-, metaand para-Xylenes anddivinyl, trivinyl and tet-ravinyl alkyl-benzenes, such as toluene, ethylbenzene, propyl benzene, ethyl, propyl benzene, and the like, whichcontain from one to four alkyl groups of any type having not more thanabout 20 and most appropriately not more than about carbon atoms. Thevarious di-, tri-, tetra-, penta-, and heXa-Vinyl, substituted andunsubstituted, anthracenes, naphthalenes, and durenes are likewisespecifically contemplated. Additional representative aromatic comonomercompounds include 4,4-divinyl azobenzene, 4,4-divinylphenylether,4,4-divinylphenyl sulfide, 4,4-divinylphenyl disulfide, 4,4'-bis(vinylphenyl amine, tris (4,4',4"-vinylphenyl) amine.

The aromatic modifying comonomers may be represented by the followinggeneral structural formula:

in which A represents any aromatic nucleus, such as a benzene,naphthalene, anthracene or durene ring; R represents any substituted orunsubstituted aliphatic, preferably alkyl, group containing at leastone, but preferably not more than 20 carbon atoms; and x is any integerfrom two to the number of positions available for substitution in thearomatic nucleus A. The R groups may be different in the same compound.

Aliphatic compounds which are specifically contemplated as modifyingcomonomers include the various acetylenes containing two or more CHgroups, specifically divinyl acetylene, diacetylene and triacetylene;diallyl acetylene, diacetylene and triacetylene; diallyl, azodiallyl,divinyl, trivinyl, diallyl and triallyl phosphates and phosphites andethylene dimethacrylate.

It is recognized in the art that the problem of cold flow is in part afunction of the inherent viscosity of the unmodified stereospecificpolybutadiene in question. As the inherent viscosity of the unmodifiedpolymer increases from the range of about 1 to 3 to the range of about 4to 5, the cold flow problem decreases proportionately. The specificrelative proportions of modifying comonomer utilized to achieve theobjects of the invention as regards dimensional stability willaccordingly vary to some extent upon the inherent viscosity of theanalogous unmodified polybutadiene, the concentration of modifier whichcan be tolerated without the production of an undesirable gel content inthe resulting polymer product, and the concentration of modifierrequisite to impart improved treadwear to tires manufactured from theresulting modified, stereospecific, rubbery polybutadiene product. Ingeneral, it has been discovered that improvement in treadwear anddimensional stability is achieved when as little as 0.025 part by weightof modifying comonomer is utilized per 100 parts total monomer weight.In the case of unmodified butadiene polymers having an inherentviscosity in the range of from about 1.25 to about 1.3, from about 0.025to about 0.4 part by weight of modifying comonomer per 100 parts totalmonomer weight, is adequate to impart dimensional stability. Preferredproportions of modifying comonomer fall within the range of about 0.05to about 0.35 part per 100 parts total monomer Weight. Normally theacceptable upper limit of not more than about by weight of gel is notexceeded when the concentration of modifying comonomer is maintainedwithin the range specified. It is important, however, when the desiredtreadwear properties and dimensional stability are obtained, to minimizegel content by maintaining the modifying comonomer concentration not inexcess of 0.2% of the total monomer weight.

While the invention is primarily concerned with modified homopolymers ofbutadiene, there is embraced within the generic scope thereof modifiedcopolymers of butadiene with all monomeric compounds having a singleterminal ==CH group. Typical comonomers contemplated include vinylmonomers such as styrene, o, m, or p-methyl styrene, the variousdimethyl styrenes, indene, vinyl pyridine, vinyl naphthalene, isobutene,acrylonitrile, allyl benzene, allyl toluene, allyl naphthalene,stilbene, methyl stilbene, 1,3-diphenyl-1-butene, isoprene,triphenylethylene, propylene, halogen-substituted derivatives of theforegoing and the like.

The invention generically contemplates the modification of all suchcopolymers in which the monomer concentrations are present in anyrelative proportion. The preferred modified copolymers of the inventioncontain from about 50% to about 99% butadiene-1,3, and from about 1% toabout 50% by weight of vinyl monomer.

The modified stereospecific polybutadiene-containing polymers of theinvention may be oil-extended in accordance with techniques known to theart for the oil-extension of SBR rubber. Such oil-extension techniquesare described, inter alia, in US. Patent 2,964,083 to Pfau et al., andin Alliger applications Ser. Nos, 132,009, abandoned in favor ofcontinuation-impart application Ser. No. 403,- 332, which was in turnabandoned in favor of pending application Ser. No. 581,423, and 132,010,abandoned in favor of continuation-in-part application Ser. No. 403,330,which is now abandoned.

The plasticizer or extension oils which can be employed in conjunctionwith the modified polybutadiene-containing rubbery polymers of theinvention are those conventionally employed in rubber compounding anddisclosed in the aforementioned Pfau et al. patent and Alligerapplications. Additionally, various liquid polymers such as lowmolecular weight, oily, hydrocarbon polymers prepared from propylene,butadiene, styrene, isoprene, and the various chlorinated andhydroxylated derivatives thereof, may be employed. Solid plasticizerscan also be used. Aromatic oils such as those known as Philrich, ShellSPX and similar commercially available products are preferred. Theplasticizers are appropriately employed in amounts corresponding fromabout 20 to 150 parts by weight, based on 100 parts by weight of themodified polymers of the invention or blends thereof with other rubberypolymeric materials.

Conventional relative proportions of re-enforcing pigments such as thevarious carbon blacks or zinc oxide are utilized in the production ofthe oil-extended or plasticized embodiments of the rubbery polymers ofthe invention. The various channel blacks and furnace blacks which arecharacterized by different levels of abrasion resistance andprocessability can be employed. High abrasion furnace blacks (HAPblacks) are preferred. The carbon blacks or similar re-enforcingpigments are appropriately utilized in an amount corresponding fromabout 40 to about 200 parts per 100 parts by weight of the modifiedpolybutadiene-containing polymer of the invention or the blends thereofwith other rubbery polymers. In the preferred practice of the inventionthe carbon black is present in an amount exceeding the quantity of theplasticizer utilized. Preferably from about 1.5 to about 12 parts byweight of re-enforcing pigment per part of plasticizer is employed. Forthe manufacture of heavy duty tire tread stocks such as truck and bustire treads, it is preferred to employ from about 50 to about 100 partsby weight of re-enforcing pigment such as carbon black, and from about15 to about 100 parts, by weight, of plasticizer, based on the totalquantity of rubbery polymer employed. Analogously, it is preferred toutilize from about 30 to about 100 parts by weight of reinforcingpigment such as carbon black per 100 parts by weight of combinedplasticizer and rubbery polymer.

The modified polybutadiene-containing polymers of the invention are usedto good advantage in the form of both two-component and multi-componentblends in all relative proportions with plastics and resins as well asother rubbery polymers. Plastics and resins suitably blended with themodified polybutadiene-containing polymers of the invention include forexample polystyrene, phenoplasts, aminoplasts, epoxy resins. Rubberypolymers suitably blended with the modified polybutadiene-containingpolymers of the invention include for example natural rubber, SBRrubber, butadiene-acrylonitrile copolymers, stereospecific rubberypolyisoprene, conventional stereospecific polybutadienes, stereospecificbutadiene copolymers and ethylene-propylene copolymers. There ispreferably employed from about 25 to about 75 parts by weight of apolymer of the type contemplated by the invention and from about 25 toabout 75 parts by weight of a rubbery polymer such as natural rubber,SBR, butadieneacrylonitrile copolymers, stereospecific polyisoprene,conventional stereospecific polybutadienes, stereospecific butadienecopolymers or ethylene-propylene copolymer. Particularly desirableresults are obtained from blends containing from about 60 to about 40parts by weight of a polymer of the invention and from about 40 to about60 parts by Weight of natural rubber, ethylene-propylene copolymer, SBR,conventional stereospecific homopolymers and copolymers of butadiene orrubbery stereospecific polyisoprene.

Additionally, the modified polybutadiene-containing polymers of theinvention are ideally adapted for conversion to graft polymers orcopolymers. Such copolymers or graft polymers are produced by subjectingthe modified polybutadienes of the invention to polymerizing conditionsin the presence of one or more olefinic materials includirig withoutlimitation vinyl chloride, the styrenes such as styrene, substitutedstyrenes, acrylonitrile, the acrylates such as methyl and ethylacrylate, the methacrylates such as methyl and ethyl methacrylate, vinylfluoride, and the like.

The ensuing examples demonstrate the superior properties imparted totire treads by the polybutadiene-containing polymers of the inventionand evidence the fact that such polymers are characterized bydimensional stability as determined by cold flow characteristicssignificantly greater than conventional stereospecific polybutadienes.

In each of the ensuing examples the flow characteristics were determinedby maintaining a 1" x 1" x 2" block of the rubber at a temperature of 25C. for 24 hours. Substantial distortion of such sample cubes isindicated in the examples by the expression flow, whereas dimensionalstability as evidenced 'by shape retention by the sample cubes isindicated in the examples by the expression no flow.

Example 1 To illustrate the improved physical properties demonstrated bythe modified polybutadienes of the invention, polymers were preparedfrom the following charges:

Parts by Weight Sample No Polymer A Polymer B Butadicne 100 100 Hexane300 300 Butyl lithium (as carbon bound 1 O. 0073 0. 0088 Divinyl benzene0.00 0.1

formulas and treads for 8.25-20 truck tires produced therefrom:

Truck tires were built and cured embodying these treads. The tires weremounted in the dual drive position, overloaded 15 percent (load per tireof 3.830 pounds) and driven for 16,000 miles on a Texas testing track at55 miles per hour. At the end of the tests, the tires were examined forwear, cracking and precut growth. The result of the testing was asfollows:

Treadl 1, Tread 2,

Control Invention Wear rating 120 Cracking Slight Slight Precut growth,inch 1. 88 1. 28

Polymer B of the invention under the rigorous test was 20 percent betterin resisting wear and 26.6 percent better in resisting out growth thanthe control, Polymer A.

Example 2 The Polymers A and B of Example 1 were also compounded in thefollowing formulas and 6.5043 passenger tire treads produced therefrom:

Parts by Weight Tread 3 Tread 4 SEE (extended with 37% pts. oil) 68.7568. 75 Polymer A (control) 50.00 Polymer B (of invention)-. 6']. 00 ISAFcarbon black 62.00 62.00 Zinc oxide 3. 00 3. 00 Ste-aric acid- 2.00 2.00

' 18. 75 18. 75 Antioxidant 2. 25 2. 25 Paralfin. wax. 2. 00 2. 00Sulfur 2. 00 2. 00 Accelerator 1. 00 l. 00

Passenger tires were built and cured embodying these treads. The tireswere mounted on the drive wheels (rated load of 835 pounds per tire) anddriven for 6,000 miles on a Texas testing track at speeds of 60 to 70miles per hour. At the end of the test, the tires were examined forWear. The results of the tests were as follows:

Tread 3, Tread 4, Control Invention Wear rating 100 Polymer B of theinvention under the conditions of test wore 15 percent better than thecontrol, Polymer A.

Example 3 not so high as to preclude processing on conventional factoryequipment.

Polymers A (control) and B (in accordance with the invention) of Example2 were compounded in the fol- 8 As indicated in the above table, SampleA which did not contain divinyl benzene in accordance with theinvention, was characterized by the cold flow to which the invention isdirected. Samples B and C containing the indicated lowing tread typecompound: trace amounts of divinyl benzene did not fiow, and fur- Partsby weight ther, neither of these samples contained an undue amountPolybutadiene 100.0 of gel. Although Samples D and E had their flowchar- ISAF carbon black 60.0 acteristics corrected, these samples, andparticularly Sam- Oil 31.0 ple E, contained undesirable quantities ofgel. Zinc oxide 3.0 10 Stearic acid 2.6 Example 5 Antioxidant 2.6 S lf13 Another serles of recipes according to the following Accelerator 13formulations were charged into polymerization reactors: 15 Thecompounded Mooney ML values of these stocks were Pam D W i ht 61 for thecontrol stock and 64 for the stock containy eg i o mer of the mention.These stocks 0th 0 im'tlngP 1y B o pt Sample No A B 0 1) 1y cured at 212F. in 60 minutes. Physical properties 0 he norm on idered in evaluatinvulca izate ft g 3 S h g d Butadlene.-- 100 100 100 100 weir; etermme ansuc properties are repor e in B t 1% 300 300 300 300 11 y 1 1111111 Ta 6I lithium 0. 0097 0.0007 0. 0097 0. 0097 TABLE I Dlvinyl benzen None0.10 0.25 0.50

Control Stock of Swck Invencon Polymerization was efiected, in eachinstance, at 50 C. N 1 t t t Polymerizations were completed afterapproximately four 725 775 hours and the polymer conversion was in eachinstance r .0 essentially 100%. The polymers were recovered from roreedi r i r at fiiefi 5 0 solution. In each instance inherent viscosity,percent gel g rarficg/lpdulus, p.S.i content and flow characteristics ofthe resulting polymer t fi t $,j-5;, M m were determined. The results ofthese determinations are Ring tear, pounds/inch, atset out in Table IIIas follows:

2%2 F 32g 322 2 20 2 Firestone Flexomet 35 TABLE III g 1:33: gg g 03mdehsan. 1113:: 20.0 20.3 Sample n n Percent Flow ph Running temperature,F 290 307 Vlscoslty Gel actenstlcs Steels]??? Rebound, percent, at- 48 2""I 'f'i'II'T'I'TIIIIIIII 1 1 77 Flows- 21 F 62 6 2 26 0.0 No Flow.

3 70 13.8 Do. 2.50 59.3 Do.

Example 4 Polymerization charges, according to the followingformulations, were introduced into reaction vessels:

Parts by Weight A B C D E 0.0121 0.0121 0.0121 0.0121 0.0121 Divlnylbenzene None 0. 125 0.250 0.375 0. 500

*Determincd by the method of H. Gilman and A. H. Haubein, J. Am. Chem.$00., 66, 1515-16 (104-1).

Polymerization was effected, in each instance, at 50 C. Polymerizationswere completed after approximately four hours and the polymer conversionwas in each instance essentially 100%. The polymers were recovered fromsolution. In each instance inherent viscosity, percent gel content andflow charaacteristics of the resulting polymer were determined. Theresults of these determinations are Example 6 Another series of recipesaccording to the following formulations were charged into polymerizationreactors:

Parts By Weight Sample No A l B l C l D l E Butadiene 100 100 100 100Hexane 300 300 300 300 300 Butyl lithium (as carbon bound llthium) I 0.0076 0.0076 0.0076 0. 0076 0.0076 Dlvinyl benzene 0.00 0. 0 0.10 .1875375 Polymerization was effected, in each instance, at 50 C.Polymerizations were completed after approximately four hours and thepolymer conversion was in each instance essentially 100%. The polymerswere recovered from solution. In each instance inherent viscosity,percent gel content and flow characteristics of the resulting polymerwere determined. The result of these determinations are set out in TableIV as follows:

TABLE IV Sample No. Inherent Percent Flow Char- Viscosity G acteristics2. 70 0. Flows. 2.13 0.00 No Flow 2. 77 0. 75 Do. 4. 09 1. Do. 2. 91 65.0 Do.

Although the whole polymer inherent viscosities of such lithiumcatalyzed polybutadienes can be regulated substantially by varying theconcentration of active catalyst, the predominant percentage of thepolymer invariably falls within an inherent viscosity range of not morethan three inherent viscosity units; more typically, at least about 90percent of any such polybutadiene falls within an inherent viscosityrange of one or two inherent viscosity units. Surprisingly, however, thepolybutadienes of the invention have quite broad molecular weight distributions and still contain essentially no gel. These facts areillustrated by the polymers prepared pursuant to the following recipes:

Parts by Weight Sample No A, Control B, Invention Butadiene 100 100 Hexane 300 300 Butyl lithium (as carbon bound lithium) 0.0050 0.007 Divinylbenzene O. 05

The polymerizations were carried out at 50 F. to 100 percent conversion.Both polymers were essentially gel free. The molecular weightdistributions of the two polymers are shown in Table V as follows:

As seen from the above data, over 90 percent of the control polymer Aoccurred in a very narrow inherent viscosity range of no more than twoand more likely one inherent viscosity unit.

What is claimed is:

1. A bend of (A) from about 175 to about parts by weight of a syntheticrubbery polymer having a polybutadiene portion which contains, asdetermined by infrared analysis, at least 30% cis 1,4 structure, a total1,4 structure of at least about 85% and not in excess of 12% of 1,2structure; said polymer prepared from monomeric mixtures consistingessentially of butadiene and from about 0.025 to about 0.4 part byweight per 100 parts by weight of said butadiene, of a comonomer havingat least two terminal =CH groups, and (B) from about 25 to about partsby weight of a rubbery emulsion copolymer of butadiene and styrene.

2. A blend as defined in claim 1, in which said commonomer having atleast two terminal =CH groups of said synthetic rubbery polymer has thefollowing structural formula:

in which A represents an aromatic nucleus, R is an aliphatic group, andx is any integer from two to the number of positions available forsubstitution in the aromatic nucleus A.

3. A blend as defined in claim 2 in which said comonomer having at leasttwo terminal :CH groups of said synthetic rubbery polymer is divinylbenzene.

4. A blend as defined in claim 1 in which the polybutadiene portion ofsaid synthetic rubbery polymer contains from about 30% to about 60% cis1,4 structure, a total of 1,4 structure of at least and not more thanabout 10% 1,2 structure.

5. A blend as defined in claim 1, in which the polybutadiene portion ofsaid synthetic rubbery polymer contains at least about 85% cis 1,4structure and not more than about 10% 1,2 structure.

6. A pneumatic tire, at least the tread portion of which comprises avulcanizate of a blend as defined in claim 1.

7. A pneumatic tire as defined in claim 6 in which the polybutadieneportion of said vulcanizate contains from about 30% to about 60% cis 1,4structure, a total 1,4 structure of at least about 85% and not in excessof 10% 1,2 structure.

8. A pneumatic tire as defined in claim 6 in which the polybutadieneportion of said vulcanizate contains at least about 85% cis 1,4structure and not more than about 10% 1,2 structure.

9. A rubbery composition comprising (A) a blend, totaling parts byweight, as defined in claim 1; (B) from about 40 to about 200 parts byweight of a re-inforcing pigment; and (C) from about 15 to about partsby weight of a plasticizer.

10. A pneumatic tire, at least the tread portion of which comprises avulcanizate of a rubbery composition as defined in claim 9.

References Cited UNITED STATES PATENTS 2,781,334 1/1957 Welch et a1.26080.7 2,847,406 8/1958 Legge 260-83.7 2,975,160 3/1961 Zelinski260-83] 3,060,989 10/ 1962 Railsback ct al 2605 3,084,084 4/1963 DAlelio26094.3 3,094,512 6/1963 Short 260-83] 3,239,495 3/ 1966 Small 26080.'73,280,084 10/1966 Zelinski et a1. 260-83.7

FOREIGN PATENTS 817,693 8/1959 Great Britain. 951,831 3/ 1964 GreatBritain.

MURRAY TILLMAN, Primary Examiner. WILLIAM H. SHORT, Examiner. M. J.TULLY, I. W. SANNER, Assistant Examiners,

1. A BEND OF (A) FROM ABOUT 75 TO ABOUT 25 PARTS BY WEIGHT OF A SYNTHETIC RUBBERY POLYMER HAVING POLYBUTADIENE PORTION WHICH CONTAINS, AS DETERMINED BY INFRARED ANALYSIS, AT LEAST 30% CIS 1,4 STRUCTURE, A TOTAL 1,4 STRUCTURE OF AT LEAST ABOUT 85% AND NOT IN EXCESS OF 12% OF 1,2 STRUCTURE; SAID POLYMER PREPARED FROM MONOMERIC MIXTURES CONSISTING ESSENTIALLY OF BUTADIENE AND FROM ABOUT 0.025 TO ABOUT 0.4 PART BY WEIGHT PER 100 PARTS BY WEIGHT OF SAID BUTADIENE, OF A COMONOMER HAVING AT LEAST TWO TERMINAL =CH2 GROUPS, AND (B) FROM ABOUT 25 TO ABOUT 75 PARTS BY WEIGHT OF A RUBBERY EMULSION COPOLYMER OF BUTADIENE AND STYRENE. 